It is generally known and accepted in the art that compounds exhibiting alpha adrenergic activity may be used for the treatment of a wide variety of diseases and conditions of the peripheric system and the central nervous system (CNS).
The alpha adrenergic receptors can be divided on a pharmacological basis into alpha1 and alpha2 adrenoceptors, which can both be further divided into subtypes. Three genetically encoded subtypes, namely alpha2A, alpha2B, and alpha2C adrenoceptors, have been discovered in human. A fourth pharmacologically defined subtype, namely alpha2D adrenoceptor, is known in some other mammals and in rodents. It corresponds to the genetically defined alpha2A adrenoceptor.
The alpha2 adrenoceptor subtypes have distinct tissue distributions and functional roles. For instance, while alpha2A adrenoceptors are widely expressed in various tissues, alpha2C adrenoceptors are concentrated in the CNS and appear to play a role in the modulation of specific CNS mediated behavioral and physiological responses.
Some compounds that are non-specific for any of the above-mentioned alpha2 subtypes and some compounds that are specific for certain alpha2 subtypes are known in the art. For example, atipamezole disclosed in EP 183 492 is a non-specific alpha2 antagonist. Compounds that are selective antagonists for the alpha2C subtype and are thus useful for the treatment of diseases of the central nervous system, are described, for example in WO 2009/013390 and WO 2010/058060.
In order to be able to reduce the risk of adverse events during treatment, an enhanced selectivity of the alpha2 antagonists would be desirable. For example, the use of non-selective alpha2 antagonists is attributed with side effects, such as increases in blood pressure, heart rate, salivary secretion, gastrointestinal secretion, and anxiety. Also an enhanced potency of the alpha2C antagonists would be desirable, in order to be able to reduce the dose needed.
DE 2241991 B2 discloses certain piperazinyl sydnonimide derivatives possessing hypotensive, vasodilatory and antianginous properties.